Antenna coupling network



Oct. 27, 1953 A. J. RUNFT ANTENNA COUPLING NETWORK 2 Sheets-Sheet 1 Filed Dec. 5, 1950 2955 fb/L /zscraasmr/c MD zan/ TM CHANNELS 72 OVM 72 E FezauENcY w MEG/IC'YCLES/JZCO/VD I N VEN TOR.

AR THUR J. RUNF T ATTOR/VE Y.

Oct. 27, 1953 A. J. RUNFT 2,657,310

ANTENNA COUPLING NETWORK Filed Dec. 5, 1950 2 Sheets-Sheet 2 Ch/ 6; 7'. "*30 30052525 WA?! down 0mm PAPA-E BASE ym/00c ,eaa

cow. :5 r "20 $005252: Me: CZ QSEWMO 1519455 EM Jl/IEZ D INVENTOR. ARTHUR .1. RU/VFT ATTORNEY.

Patented Oct. 27, 1953 STATES PM Em" o 2,657,310!

ANTENNA? GEUPLINGS NETWORK Ant-bur. .1;v Hunt-37;} Cincinnati, Ohio,v assigpon tor Avcm Manufacturing; Corporation, Cincinnati; flliib aoonporatibn Delaware AhpiicatioinDecemiier 5, 195031Se1i21' i ioi19'9g241i y i-Claimsa 1 My: inventiom relaxes broadly: to; passive netwbrksiandiin:particularzttrarhighzfrequencgtmag; r'reticaiiy cnup'iedi triple-timed receiver: input system;-

Doub'IeI-tunew receiverinnutcircuitsmavez been used in the prior art. However, vemlittl-ezwork seems= t'cr Have: been done: in? connection-i Within]- creasingthe :seiectivitwaind averageegaim of such circuitsm combination with: a mditype. ofz'bui1t1- inantenna? Especiailwis this? true in theitei-e; vision-art? It is a primary 0153' ect of! myinvention: totp'r vide -a'zi' Ea tuner iiiput system whichtwill have a-substantially=-*unirormzresponsestwrauiated sige nan-m ade'sired passmandisaid signais beingsree ceive'd on either a single -built-in r-od' typefiof "amtenna or cn awbaianced externaiityne of'antenna'.

11:5 is aio' an object offmwinventionl ttrprovide anew and improved circuitlfonccupiinna single buiit-in rod antenna or 'a" conventional iba-ianced 1 externai antenna to t'i'ie' amplifier. on com v-erter tube iira teieviion receiveri It is a-= stillfurther" object of invention: to provide a new and improved means for coupling a -built inercd type ofantnna to an inputicircuit in such a manneras-tc provide degree of skirt attenuation'aswe11 as a' higlienavemge gaih than-i'provided by circuits cf tlie prionart provide" at doubie tuned over c'oupied antenna.

transformer designed for 72 ohm balanced' 'input' anda'hi'gh'iinp'edance singie= ended output} which functions with a buiit -in rod type of antenna-in s'ucH- aI=- manner asF ttf'form a triiI1e=tim'el'i input circuit For a better understaardiirg?of tfreepresent?in ventio'n; togetherwith ctiier andniirtherofijects, advantages" and cap'abilitiestfierecfi reference is madeto: the following disclosure X anti appended. claims; in connection witii the accompanying drawings; inwhioh Fig. 1 is a circuit diagram of my triple-tuned input. circuit showing the; points; at which. the circuit. isionenedifor adjiistingmach.tunedicircuit;

Fig. '2 is. an. equiilalent; diagram. offtfier circuit showni'nFig. .1;

Fig. 3 is a curve showing the response and bandepassicharacteristics ofethecircuit'iniFig- 1 when usedlin conjunction witharodtype builtin antenna.

Figs. 4, 5, 6 and 7 show:thancompfeuents-r from which. at specific: coupling; tramstormerf" assembled;

Referring to Fig. 1, I have. thertnshowna portion of a television redrawn circuit? 'cal double-humped gain characteristic 2 porating a specific embodiment of my invention; A rod. type antennailiistconnected to one termi= naliof a balanced antenna input plug 2. The baiancedante'nna i'nput pIugZ is connectedtfirough transmissiorr line 3*" to" the primary 4 of air over coupled? input transfbrmeriir such an manner as: to alibw-theuse ofeitiierabaianeed antennae not shown; ora ro d typ'e' -antenna; such' as antenna l riapacitor'ffi whichisconnectewa'eross=priinary 4, is provided for tuningrtiie primary circuit An electrostatic" shield (i effectively eliiniiiate's catpacitive cc upi'ing betwe'enprimary winding flan-d seconuam-windingTi The-secondary winding i is 't'uned toband center by capacit'or t inser-ieew-itii the inputcapacitance oftubeI 0 5 wliiclrmi'ght be eitfieranR. F. ampiifl'er'or'the converter: Aiso:

unbalanced input-system 'I-ha shield 6: is aiso connectedtoground? Ifisfiould now b'e obvioustliatt the circuit which has so far been described; witl r trier-exception: of antenna l, is essentially a"- double tuned mag neticail'ynvercoupled input circuit; havinga t'y-pi How;- ever? when antenna I is connectedii'rto the==sys= 1 term andthe'wariouscircuits are timed inwa marrn'e'rf to be iiereinaft'er' explained? a triplex-tuned magnetically overcoupled systenrobtainsi In" Fig: 1 there are three circuits which' are tuned-tome approximate geometrivmeamwof tiie selected band -pa'ss frequency: clbsed pri"- mam loop including capacitor 5 constitutes the iirsuo'ffthesetiireetuned=circuitsr Tire-secondary T along? witfr capacitor 8' in" series 'witii the input capacitance 9* ortube Wmalres up the secomr or the*tir'iree*tunedicircuits? THe effect-iye c'apacitite reactance ti) ground of antenna l and one leezd of'tranmission line"3 irrcombination witiithe infiductance of one half of grounded primary 4 makes up: the third? anddast of tl'ratiireetimed w circuits; It? shoul'dibe' noted that? transmission lineiafisznot necessary ifither antenna connections aimimadee d'iiiectly tdtpriinaryi winding, 4',

The-:firsttwor0fr.the -aboyementioneditunediciricuitsiiorm-adouble-tuneofflcoupling: circuit which mustsbercapableof nassingiaigiven fizeqnency band when used with a balanced external type of antenna. The band width of the double-tuned transformer is primarily dictated by the bandpass requirements for connection to the balanced external type antenna and, as will now be shown, there is only one design coupling variable, K1, which is available to determine the band-pass characteristics of the circuit when it is used with a built-in rod antenna 1.

Any two circuits which are coupled by a common impedance must have a coemcient of coupling K equal to the ratio of the common impedance to the square root of the product of the total impedances of the same type as the common impedance, which are present in the coupled circuits. In other words, if Zm is the common impedance between two coupled circuits and Z1 and Z2 represent the total impedances of the same type in the coupled circuits, then Z L V 1Z2 Using Equation 1, the coupling coeflicient K1 of the circuit of Fig. 1 can now be developed from the equivalent circuit diagram Fig. 3, where Ra represents the resistance of rod type antenna i; Ca represents the series capacitance of antenna 4 1.1a represents the series inductance of antenna I; L1 represents the inductance of one half of primary winding 4; M1 represents the mutual inductance between the two halves of the primary winding 4; M2 represents the mutual inductance between the primary 4 and the secondary I and and L2 represents the inductance of secondary 1. Substituting the values of Fig. 3 in Equation 1, it can be seen that,

In other words, increasing the turns on pri mary 4, that is increasing L1, with the resultant increase in M1 along with decreasing the antenna rod length, that is, decreasing La, tends to increase the coupling coefficient K1, thereby increasing the responsive band width of the system when it is used with a rod type of antenna.

It may not always be convenient to adjust the length of antenna l in order to realize the correct antenna inductance La. Therefore I have included an inductance coil IL, in the circuit diagram of Fig. l which can be used to add in-- ductance in the antenna circuit, if it be necessary to keep antenna I so short, because of cabinet design, that the antenna itself does not furnish sufiicient inductance.

In Figs. 4, 5, 6 and '7 I have shown the coil data used in a specific embodiment of Fig. l. The complete transformer was assembled by first placing secondary coil, Fig. 4, inside of the coil form Fig. 5. The brass foil shield, Fig. 7, was first covered with a thin sheet of insulating material so that it could not act as a shorted turn, magnetically speaking, and then it was wrapped around the outside of the coil form. Then the primary coil, Fig. 6, was placed over the brass shield.

The design of the transformer can be checked by testing the resonant frequency of each tuned circuit separately. Though variable capacitances are not used in the circuit and though it is not practical, because of the long lead length required, to use a variable capacitance for testing pur-- poses in each tuned circuit, various capacitances may be connected into place until the correct capacitance is found that will cause the tuned circuit under test to resonate at the proper frequency. The resonant frequency of the tuned circuits in Fig. 1 may be each checked separately in the following manner:

1. The primary and secondary circuits are opened at terminals X and Z. The circuit which comprises antenna rod I, one lead of transmission line 3 and one half of primary 4 is then tuned as a loaded quarter-wave configuration by adjusting the length of antenna red I to the geometric mean of the given band frequency. Tuning may be done by observing the dip in a megacyclemeter coupled to the grounded (high current) end of the rod or to the lead-in transmission line tape.

2. Next, terminal X is reconnected and terminals Y and Z are opened. The primary resonance of capacitor 5 and winding 4 is then adjusted at the geometric mean of the given frequency band.

3. Then, terminal Z is reconnected and terminals X and Y are opened. The circuit comprising secondary 1 along with capacitor 8 in series with input capacitance 9 is then adjusted to resonate at the geometric mean of the given frequency band.

After the circuits of Fig. l are tuned and properly connected for operation with a rod type antenna, a triple-tuned, overcoupled band pass response to radiated signals obtains and three resonant frequency peaks distributed across the band pass are indicated when the circuit is tested with a megacycle meter. In a specific embodiment of the circuit of Fig. 1, using a transformer made up from the components shown in Figs. 4, 5, 6 and '7, the units were tuned to the geometric mean of a frequency band extending from 54 megacycles to 88 megacycles. As can be seen in Fig. 3 the three peaks occur at approximately 57, 72, and 84 megacycles to give a resultant characteristic having greater average gain in the pass band and greater skirt attenuation than would be possible with a conventional double-tuned circuit.

Thus it will be seen that I have provided a circuit combination comprising a double-tuned electrostatically shielded magnetically overcoupled input circuit having a primary winding which is center tapped to ground (4, 5, 6, 1, 8, 9 and Ill), a non-refiecting transmission line 3 connected to said input circuit, one side of said transmission line 3 and one half of said primary winding 4 having such a reactance as to form a resonant configuration tuned to the geometric mean of a given frequency band when connected to a rod type antenna I.

While I do not desire to be limited to any specific circuit parameters such parameters varying in accordance with individual designs, the following circuit values have been found entirely satisfactory in the illustrated embodiment of the invention:

-lApproximately 37" of #1 tinned copper buss (shorter if used with series inductance as loading coil) (controls value of La).

3-3V inches of '72-ohm balanced transmission line.

l-Goil as shown in Fig. 6 (plain copper wire may be used in lieu of sodereze as shown on drawing).

5-33 micromicrofarads.

'i-Coil as shown in Fig. 4 (plain copper wire may be used in lieu of sodereze as shown on drawing).

833 micromicrofarads.

9-Input capacity of one 12AT7 section plus wiring (approximately 5 micromicrofarads).

I0-One triode section of a 12AT7 tube operated as a converter.

While there has been shown and described what at present is considered the preferred embodiment of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention as defined by the appended claims.

Having thus described my invention I claim:

1. In a receiver the combination comprising a double-tuned electrostatically shielded magnetically over-coupled input circuit having a primary winding which is center-tapped to ground and tuned to the geometric mean frequency of a given frequency pass-band and a secondary winding tuned to said geometric mean frequency, a non-' reflecting transmission line connected to said input circuit, one side of said transmission line and one half of said primary winding having reactance parameters which form a resonant configuration tuned to the geometric mean of said frequency band when connected to a rod type antenna having inherent reactance to ground.

2. In a receiver for receiving signals over a given frequency band, the combination comprising a center-tapped primary and a secondary winding connected to form an overcoupled doubletuned input system having two tuned circuits each being tuned to the geometric mean frequency of a given frequency band, a transmission line connected between said input system and a balanced antenna input plug, one-half of said centertapped primary and one side of said transmission line being tuned with a rod type antenna to the geometrical mean of said given frequency band, whereby the input system when attached to said rod antenna forms a triple-tuned circuit.

3. In a receiver for receiving signals over a given frequency band, the combination comprising a capacitor tuned primary winding and a secondary winding being connected and adjusted to form an overcoupled double-tuned input circuit wherein the primary and secondary windings are each tuned to the geometric mean frequency of a given frequency band, said primary winding being center-tapped to ground, a transmission line connecting said input circuit to a balanced antenna input plug and a rod type antenna connected to one terminal of said plug, one-half of said center-tapped primary and one side of said transmission line being tuned with said rod type antenna to the geometrical mean of said given frequency band, whereby the input circut when attached to said rod antenna forms a triple-tuned circuit.

4. In a receiver for receiving signals over a given frequency pass-band the combination comprising a first circuit tuned to the geometric mean frequency of said given frequency pass-band consisting of a capacitor tuned primary winding having a grounded center-tap, a second circuit tuned to the geometric mean frequency of said given frequency pass-band which is magnetically overcoupled to and electrostatically shielded from said primary winding consisting of a capacitor tuned secondary winding, and a third circuit tuned to the geometric mean frequency of said pass-band frequency comprising a rod-type antenna, one side of a transmission line, one-half of said primary winding and the inherent antenna reactance to ground.

5. In a receiver for receiving signals over a given frequency pass-band the combination comprising a first circuit tuned to the goemetric mean frequency of a given frequency pass-band consisting of a capacitor tuned primary winding having a grounded center-tap, a second tuned circuit tuned to the geometric mean frequency of said given frequency pass-band which is magnetically over-coupled to and electrostatically shielded from said primary winding consisting of a capacitor tuned secondary winding, and a third circuit tuned to the geometric mean frequency of said pass-band frequency comprising a rod-type antenna, one-half of said primary winding and the inherent antenna reactance to ground.

ARTHUR J. RUNFT.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,703,171 Purington Feb. 26, 1929 1,901,025 Franklin Mar. 14, 1933 1,995,152 Loftis Mar. 19, 1935 2,116,696 De Monge May 10, 1938 2,215,810 Fener et al Sept. 24, 1940 2,223,825 Holst et a1. Dec. 3, 1940 2,512,481 Cohen June 20, 1950 

